South Korean and U.S. officials have implicated North Korea in the attacks, though have offered little evidence to back up their claims.

Seoul's National Intelligence Service has said the outages, which involve multiple computers trying to connect to a single Web site at the same time, thus overwhelming the server, were likely carried out "at the level of a certain organization or state."

Three U.S. officials said Wednesday that while Internet addresses have been traced to North Korea, that does not necessarily mean the attack involved Kim Jong Il's government in Pyongyang. They spoke on condition of anonymity because they were not authorized to speak publicly on the matter.

South Korean lawmaker Chung Chin-sup, a member of the National Assembly's intelligence committee, cited an earlier North Korean warning to South Korea as implicating Pyongyang in the cyber attacks.

Last month, North Korea accused the South of planning to participate in U.S.-led exercises known as "Cyber Storm," calling it an "intolerable provocation."

North Korea was "fully ready for any form of high-tech war," a spokesman for country's Committee for the Peaceful Reunification of Korea said in remarks carried by the official Korean Central News Agency on June 27.

"As universally recognized, the U.S. is the kingpin of 'cyber attack' and 'hacker intrusion' on our planet and South Korea is not an exception," the unidentified spokesman said.

"Cyber Storm," a war game sponsored by the U.S. Department of Homeland Security, began in 2006 and simulates a federal response to a major cyber attack. The most recent version was held last year.

North Korea, which regularly accuses the U.S. and South Korea of plotting to attack it, said the U.S. seeks to use the exercises to mount "pre-emptive attacks on the anti-U.S. and independent countries."

Chung, a member of the ruling party, said he believes North Korea is behind the latest cyber attacks. He said they were another tactic by the North to draw U.S. attention and strengthen its bargaining position.

North Korea wants diplomatic relations with the U.S., lifting it to the same status as rival South Korea, and aid for its impoverished economy.

Park Young-sun, a lawmaker who is also a member of the intelligence committee, said a senior intelligence official told her the NIS suspects the North because of the warning last month, according to a statement from her opposition Democratic Party.

Her party has been critical of the NIS, saying its finger-pointing at the North is an excuse to drum up support for anti-terrorism bills that have been pending for months in the National Assembly.

Park also told a party meeting that the NIS official who briefed her noted most of the attacked Web sites were those of conservative South Korean organizations that have pushed for a hard line on North Korea.

Besides the presidential Blue House, the conservative ruling Grand National Party also was a target.

The spy agency said it could not immediately confirm Park's remarks.

Some in South Korea were beginning to show irritation at the lack of clear evidence.

The Seoul Shinmun newspaper ran an editorial urging the government to "thoroughly find out who is behind the terror," adding it is "not clear yet who is involved."

The government "should first determine whether North Korea is the origin of the attacks or if they were committed by a simple hacker and then try to get the international community to study corresponding measures," the newspaper said.

The attacks have grabbed headlines and raised the alarm over the possibility for disruption of key computer networks. But there has been no broader panic or social chaos — South Koreans have gone about their business as usual.

Graham Cluley, senior technology consultant at Britain's Sophos PLC, said that if the attacks have been orchestrated by North Korea, they would "stand out as a particularly bold attack — but I would counter that by questioning whether it wasn't also pointless."

He said so far all that has been achieved was to make it harder to visit a few Web sites.

"They haven't — as far as we know — managed to steal any information, they haven't defaced the sites and posted propaganda, they aren't likely to have impacted the economy of (South) Korea or the USA through their actions, or disrupted the military," he said.

In Italy, Japan urged other Group of Eight countries to step up pressure on North Korea.

Japanese Foreign Ministry press secretary Kazuo Kodama, asked about the cyber attacks, said it was important for the rest of the world, led by the U.S., Japan, and the G-8, to "send out a single, strong message" to Pyongyang that it "should not continue these provocative actions to pose a threat to the region."